The present invention relates to over-voltage protection for power supplies. More specifically, the present invention relates to conditional over-voltage protection for redundant phase-shift converters.
A typical switching power supply has a switching stage, such as a pulse width modulator or phase-shift controller to regulate the output voltage of a power stage. Over-voltage protection is achieved by comparing the output voltage of the power stage to an internal over-voltage reference. When an over-voltage condition is detected, the switching is disabled which disables the power stage shutting down the output voltage.
In a redundant power system multiple power supplies are connected to a common bus to maintain availability of the bus voltage in the event of failure of one of the contributing supplies. An over-voltage condition of one power supply can raise the common bus voltage causing activation of the over-voltage protection of the other power supplies connected to the common bus.
In a low current redundant power system each power supply output is connected to the common bus through a diode, commonly referred to as an "OR-ing" diode. The "OR-ing" diode prevents each supply from sensing the over-voltage conditions of other supplies. An over-voltage bus reverse biases the diodes of the working supplies. Only the faulty supply is latched off by its over-voltage protection. Once the over-voltage condition is thus removed the remaining supplies resume normal operation.
In high current redundant systems it is not practical to use "OR-ing" diodes because of the severe loss of efficiency. All the supplies will sense an over-voltage fault in any supply and latch off causing unavailability of bus voltage.